1. Field of the Invention
The present invention relates to a CVD apparatus, and more particularly, to a CVD apparatus in which a chemical vapor deposition process (CVD process) as one of the processes for manufacturing semiconductor devices is carried out. The CVD process is a method of depositing a thin film onto a substrate through chemical vapor phase growth.
2. Description of the Related Art
Recent manufacturing processes for semiconductor devices tends to advance integration and miniaturization of electronic circuit elements incorporated in the semiconductor devices. The miniaturization of the elements in the manufacturing process requires new techniques. For example, techniques for sufficiently filling fine holes with film, reducing the steps caused on the elements, reducing heat generation due to high current density, or preventing breaking of wires by electromigration are required. As one of the manufacturing processes meeting such technical requirements, in place of the sputtering process depositing an aluminum film, a thermal CVD (chemical vapor deposition) process attracts attention, which uses WF.sub.6 (tungsten hexafluoride) gas and H.sub.2 gas to deposit a blanket tungsten (W) film (hereinafter referred as a "B-W film"). When such a B-W film is used, sufficient step coverage characteristics can be attained even for a hole with a diameter of 0.5 .mu.m or less and an aspect ratio of 2 or more. Thus, the thermal CVD process can satisfy the above requirements such as for flattening of elements, and for prevention of breaking of wires by electromigration.
On the other hand, the manufacturing process of the semiconductor device recently requires the B-W film to be deposited on the entire surface of the substrate based on the following reasons.
In the conventional CVD apparatus, when a TiN film is deposited onto the substrate as an underlying film by sputtering, a field on which the TiN film is not deposited is formed at a place close to a periphery of the substrate, because the deposition of the TiN film is restricted by a holding structure near the periphery. Accordingly, on the occasion of subsequently depositing the B-W film onto the TiN film, the whole of the periphery of the substrate is covered with a clamping member, which presses down some discrete spots on the periphery so as to clamp the substrate, so that the B-W film can be deposited on only the TiN film. But, the above structure wherein the clamping member clamps the substrate has posed various problems. These problems include, for example, thermal lowering at parts of the substrate in the vicinity of the clamping member, film peeling off due to non-uniformity concerning the density or flow of an introduced reactive gas, dust generation due to physical and direct contact between the substrate and the clamping member, and a lowering Of the reliability due to the mechanical complexity of the movable sections.
Then, in order to solve those problems, non-mechanical clamping devices such as a vacuum chuck or an electrostatic chuck were proposed. These clamping devices made it possible to deposit the B-W film on the whole surface of the substrate, because they do not have the direct contact sections such as the above conventional mechanical holding structure.
Further, from another point of view, the aforementioned whole surface film deposited on the substrate has such an advantage that the number of device components produced from the substrate can be increased, because the available area on the substrate could be enlarged.
Next, one example of the conventional CVD apparatus depositing the B-W film on the whole surface of the substrate will be explained concretely by referring to FIGS. 7-9 in order to discuss some problems thereof. The conventional CVD apparatus shown in FIG. 7 has been actually described in U.S. Pat. No. 5,374,594.
In the CVD apparatus, a reactor 71 is provided with a reactive gas supply plate 72 at an upper region and with a substrate holder 73 at a lower region. The substrate holder 73 holds a substrate 74 on a top surface thereof. The plane shape of the substrate holder 73 is preferably circular.
A plurality of gas outlets are formed in a bottom surface of the reactive gas supply plate 72. A reactive gas supplied by a gas supply pipe 72a is blown off through the gas outlets and introduced into the reactor 71. The bottom surface of the reactive gas supply plate 72 faces the surface of the substrate 74 placed on the substrate holder 73. The reactive gas supplied through the reactive gas supply plate 72 deposits a desirable thin film onto the surface of the substrate 74 based on a chemical reaction thereof. Unreacted gas and by-product gas remaining in the reactor 71 after the film deposition process are evacuated through an evacuation section 75.
At a center section of the substrate holder 73 a passing-through hole 76 is formed in a vertical direction. The passing-through hole 76 is connected to an evacuation section 77 used for a differential pressure chuck. This evacuation section 77 for the differential pressure chuck is different from the aforementioned evacuation section 75 for the reactor 71. Some differential pressure grooves 78 are formed on a specific area in the top surface of the substrate holder 73. The specific area is a section on which the substrate 74 is placed, and the differential pressure grooves 78 are connected to the passing-through hole 76 (by passages not shown). The differential pressure grooves 78 include some straight line grooves directed in a diameter direction and some circular grooves arranged as concentric circles. When the substrate 74 is put on the substrate holder 73 and thereafter the differential pressure grooves 78 are evacuated, differential pressure can be generated between any one of the differential pressure grooves 78 and the opposite side of the substrate 74 to clamp the substrate 74 onto the substrate holder 73. The above-mentioned structure for clamping the substrate 74 is usually referred as a differential pressure chuck or a vacuum chuck.
A quartz window 79 having a cylindrical section 79a at the center thereof is provided in a bottom wall 71a of the reactor 71. The cylindrical section 79a has an end wall 80 at a lower opening, which has a cylindrical body 81 with the inside and outside double-walls. The cylindrical body 81 is closed by a bottom wall at a lower part and is provided with a connecting body 82 at an upper part. The inside cylindrical wall of the cylindrical body 81 forms a hole section connecting to the passing-through hole 76. A lower end portion of the inside cylinder is extended to the outside through the bottom wall of the cylindrical body 81. A purge gas is supplied into a space between the inside and outside cylindrical walls of the cylindrical body 81 through a purge gas introduction section 83. In the aforementioned connecting body 82, a hole connecting to the passing-through hole 76 is formed at the center thereof and a plurality of purge gas supply passages 84 are formed at the periphery thereof.
The above-mentioned substrate holder 73 is clamped on the cylindrical body 81 by means of the connecting body 82 supporting the substrate holder 73. In accordance with such a supporting structure, the substrate holder 73 is arranged at a lower and central part of the reactor 71. Three members, that is, the substrate holder 73, the connecting body 82, and the cylindrical body 81 are united as one by welding or the like. The hole 76 or the like forming the differential pressure chuck, the purge gas supply passages and the inside space of the reactor 71 are mutually separated in accordance with the above structures.
Further, in the top surface of the substrate holder 73, a purge gas blowing channel 85 having a circular shape is formed. In addition, a plurality of purge gas passages 86 connecting each of the purge gas supply passages 84 in the connecting body 82 and the purge gas blowing channel 85 are formed within the substrate holder 73 in a diameter direction thereof. The number of purge gas supply passages 84 in the connecting body 82 or purge gas passages 86 in the substrate holder 73 is eight e.g., and the eight purge gas supply passages 84 and the eight purge gas passages 86 are arranged at equal angles in the circumferential direction with respect to the center of the substrate holder 73. The depth direction of the purge gas blowing channel 85 is perpendicular to the top surface of the substrate holder 73, and an outer wall-surface 85a of the channel 85 is located within the peripheral edge of the substrate 74 placed on the top surface of the substrate holder 73. Each of the above purge gas passages 86 has an outlet opening onto an inner wall-surface 85b of the channel 85.
A cylindrical shield member 87 clamped on the bottom wall of the reactor 71 is arranged around the substrate holder 73. The shield member 87 is approximately as high as the substrate holder 73. The shield member 87 forms spaces under and around the substrate holder 73. The spaces are used as passages for passing another purge gas introduced through another purge gas introduction section 88.
An annular lamp support member 89 with reflectors is disposed below the reactor 73. A plurality of heating lamps 90 are mounted on the lamp support member 89 at substantially equal spacing. Radiant heat generated from the heating lamps 90 is provided to the substrate holder 73 through the quartz window 79 in order to heat the substrate holder 73. The substrate 74 is heated by the heat conducted from the substrate holder 73. The temperature of the substrate holder 73 is measured by a thermocouple 91 embedded therein, and thereafter measured data is used for controlling the temperature of the substrate holder 73.
In accordance with the above-mentioned configuration, the reactive gas is introduced into the reactor 71 through the reactive gas supply plate 72 facing the substrate 74, and a desirable film is deposited onto the substrate 74 on the basis of the chemical reaction. The unreacted gas and by-product gas generated in the reactor 71 are evacuated by the evacuation section 75. While depositing the film on the substrate 74, the purge gas is supplied into the reactor 71 through the purge gas introduction section 83, the purge gas supply passages 84, the purge gas passages 86 and the purge gas blowing channel 85. The purge gas blown off from the peripheral region around the substrate 74 prevents the film deposition on the rear surface of the substrate 74. The purge gas introduced into the purge gas blowing channel 85 is blown off toward the inside of the reactor 71 through a clearance 92 between the substrate 74 and the substrate holder 73 and thereby prevents the reactive gas from entering the back space of the substrate 74. In addition, a different purge gas is supplied into the reactor 71 through the purge gas introduction section 88 and the purge gas passages which are configured by the substrate holder 73, the quartz window 79 and the shield member 87. The different purge gas blown off from the region around the substrate holder 73 prevents a film deposition on the quartz window 79 and the substrate holder 73.
On the other hand, the films having been deposited on the substrate holder 73 or the like can be removed by a RIE cleaning process at every film deposition process or every lot.
Ordinary conditions for the B-W film deposition at the first stage of generating initial formation cores in the aforementioned CVD apparatus are a 2-10 sccm flow rate for the reactive gas WF.sub.6, a 2-10 sccm flow rate for SiH.sub.4, a 100-500 sccm flow rate for the purge gas (Ar), 400.degree.-500.degree. C. for the film deposition temperature, and 0.5-10 Torr for the film deposition pressure. Then, the conditions for a thick film being deposited by reduction of H.sub.2 are a 50-200 sccm flow rate for the reactive gas WF.sub.6, a 500-2000 sccm flow rate for H.sub.2, a 300-1000 sccm flow rate for the purge gas Ar, 400.degree.-500.degree. C. for the film deposition temperature, and 30-70 Torr for the film deposition pressure.
Next, another example of the conventional B-W film CVD apparatus will be explained by referring to FIG. 8. In FIG. 8, components being substantially identical to those of the CVD apparatus shown in FIG. 7 shall be designated by the same reference number and will not be explained in detail.
The conventional CVD apparatus shown in FIG. 8 also has the reactive gas supply plate 72 at an upper region and a substrate holder 93 at a lower region in the reactor 71. In the substrate holder 93, the differential pressure grooves 78 are formed on the top surface and the vertical passing-through hole 76 is formed at the center thereof. The differential pressure grooves 78 are connected with the passing-through hole 76 (by passages not shown). The quartz window 79 is fitted to the bottom wall of the reactor 71 and further a cylindrical support body 94 is clamped to the center of the quartz window 79. The aforementioned substrate holder 93 is clamped to the upper section of the cylindrical support body 94 with several screws 95. The passing-through hole 76 of the substrate holder 93 is connected to a central hole of the support body 94 so as to communicate with the evacuation section 77 for the differential pressure chuck. The lamp support member 89 with the heating lamps 90 and the reflectors are arranged below the quartz window 79. Further, the end wall 80 is provided with the purge gas introduction section 88.
The substrate 74 placed on the top surface of the substrate holder 93 is clamped by the aforementioned differential pressure chuck system.
A ring plate 96 is arranged around the top surface of the substrate holder 93 so as to cover the peripheral area of the top surface by the whole inner edge portion thereof. The ring plate 96 is supported by a plurality of vertical-direction movable support rods 97 and therefore can be moved in the vertical direction in accordance with the action of the rods. To be exact, the ring plate 96 is placed in the vicinity of the periphery of the substrate 74 clamped on the substrate holder 93. The inner edge portion of the ring plate 96 and the outer edge portion of the substrate 74 are overlapped with each other with a clearance 100 between them. Further, a cylindrical shield member 98 is disposed around the ring plate 96. The shield member 98 has a seal ring 99 on an upper rim thereof. If the ring plate 96 is moved to its lowest position, the bottom surface of the outer edge thereof contacts with the seal ring 99. When the ring plate 96 is placed at the lowest position, a passage where the purge gas introduced by the purge gas introduction section 88 flows is formed on the basis of the structure configured by the bottom wall of the reactor 71, the quartz window 79, the shield member 98, the ring plate 96, and the substrate holder 93. The purge gas introduced into the reactor 71 is blown off through the predetermined clearance 100 formed between the ring plate 96 and the substrate 74. This structure can prevent the film from being deposited on the rear surface of the substrate 74, because the purge gas blown off from the clearance 100 prevents the reactive gas supplied by the reactive gas supply plate 72 from entering the space behind the substrate 74.
The reason for causing the ring plate 96 to be movable in the vertical direction is to obtain a purge gas of a desirable blow-off rate through the clearance 100, which does not have any effect on the distribution of the film deposited on the substrate 74, by controlling the position of the ring plate 96 covering the outer periphery of the substrate 94.
An experimental result which has been obtained by the experimental apparatus shows that the film can not be deposited on the rear surface when the blow-off rate of the purge gas is included within the range of 50-700 cm/min, under the ordinary conditions mentioned below. This means that, when the clearance 100 is 0.2 mm, the flow amount of the purge gas is about 50-700 sccm on the condition of depositing the film onto a substrate of 6-inch diameter. The distribution of the film deposited on the 6-inch substrate, which is deposited within a circular range whose radius is less than the radius of the 6-inch substrate by 10 mm, is included within the range of 2-3%.
Ordinary conditions for the second conventional apparatus as to the B-W film deposition at the first stage of generating initial formation cores are a 2-10 sccm flow rate for the reactive gas WF.sub.6, a 2-10 sccm flow rate for SiH.sub.4, a 100-300 sccm flow rate for the purge gas (Ar), 400.degree.-500.degree. C. for the film deposition temperature, and 0.5-10 Torr for the film deposition pressure. Then, the conditions for a thick film being deposited by reduction of H.sub.2 are a 50-200 sccm flow rate for the reactive gas WF.sub.6, a 500-2000 sccm flow rate for H.sub.2, a 300-7000 sccm flow rate for the purge gas Ar, 400.degree.-500.degree. C. for the temperature of the substrate holder, and 30-70 Torr for the film deposition pressure.
The conventional CVD apparatus explained as the first example poses the following problems. When blowing off the purge gas toward the whole outer periphery of the substrate 74 through the clearance 92, the purge gas is apt to be blown off under the state that it concentrates at spots respectively corresponding to the outlets of the purge gas passages 86 for supplying the purge gas into the circular purge gas blowing channel 85. Consequently, since the purge gas blown off from the clearance 92 can not be uniform along the circular purge gas blowing channel 85, there are some purge gas weakly-blown off regions in which film deposition on the rear surface of the substrate 74 does occur. FIG. 9 shows the state such that the films are deposited on the rear surface of the substrate 74. There are generally eight purge gas passages 86, and accordingly eight regions on which the W (tungsten) film 102 is deposited are produced. Each of these eight regions is formed between each two neighboring spots 101 which respectively correspond to the purge gas passages 86.
On the other hand, even if the flow amount of the purge gas is increased in order to sufficiently supply it to the relatively weak blow-off regions, the relationship between strong and weak blow-off of the purge gas is maintained, and the phenomenon causes the temperature of the substrate to decrease and the density of the reactive gas at the spots where the purge gas is blown off strongly is reduced. Consequently, the distribution of the film deposited on the surface of the substrate 74 is reduced.
Further, if the flow amount of the purge gas blown off through the clearance 92 is increased furthermore, the substrate 74 easily slips off the substrate holder 73, because the purge gas produces force in a direction perpendicular to the substrate 74. Especially, when the film deposition pressure is 10 Torr or less and the flow amount of the purge gas is increased, the state of the substrate placed on the substrate holder becomes unstable, because the differential pressure between the upper side of the substrate and the differential pressure channel become smaller. The state will become more unstable when introducing the gas or performing the evacuation process after the film deposition process.
In addition, the conventional structure of uniting the substrate holder and the support section which connects the substrate holder and the evacuation section for the purge gas supply section or the differential pressure chuck poses a problem as to maintenance. That is, it is difficult to clean the substrate holder or release it for exchange.
The conventional CVD apparatus explained as the second example poses the following problems. This conventional apparatus having the mechanism moving the ring plate 96 upward or downward has three problems. The first one is that the mechanism is apt to be complicated. The second one is that the mechanism is a cause of generating undesirable particles or dust. The third one is that the throughput is reduced due to the time used for the upward or downward motion of the ring plate.
The problem as to the complexity of the mechanism is due to the necessary structure for the upward and downward moving mechanism and a driving mechanism. Further, the complexity problem is increased by the need for the structure for forming the purge gas passages, and the structure for maintaining airtightness between the purge gas passages and the inside of the reactor. The complexity of the mechanism causes lowering of maintenance and operating efficiency.
The problem of particle generation is due to the mechanical movable sections. The motions of these sections cause the generation of particles in the reactor and the reduction of a yield rate in manufacturing semiconductor devices. Especially, particles are easily generated when depositing films on the ends of the ring plate 96.
The reason for the problem of reduction in throughput is as follows.
The throughput is totally determined by the amount of time required for depositing the B-W film on the substrate and for carrying the substrate in the reactor. The amount of time for depositing the B-W film is normally about 4-5 minutes. On the other hand, in the second conventional CVD apparatus, the substrate must be kept at a standstill during the upward and downward motion of the ring plate 96. Thus, since the amount of time for carrying the substrate is increased, the throughput is reduced.